1. Field of the Invention
The present invention relates to a semiconductor optical device and a method for manufacturing the semiconductor optical device.
2. Related Prior Art
The Japanese Patent application published as JP-2003-264334A has disclosed a semiconductor laser diode that provides a substrate with a mesa formed on the mesa and a buried layer burying the mesa. The laser diode further provides trenches in the buried layer. The Japanese Patent published as JP-2004-128360A has also disclosed a laser diode with trenches in the buried layer. The trench in this patent is filled with resin and the upper electrode of the laser diode is formed directly on the resin, accordingly, the parasitic capacitance formed between the upper and lower electrodes may be reduced.
Conventionally, the trench in the buried layer is used to be formed by, what is called, the wet etching. However, the trench reaches the semiconductor substrate and the depth thereof becomes a few micrometer or larger. To form such deep trench by the wet etching has been quite hard to precisely control the etching condition thereof. Therefore, the dry etching such as the reactive ion etching (RIE) has been proposed to form the deep trench. Although the dry etching enhances the controllability of the etching, it forms the trench with steep side surface and, when the interconnection is formed over the trench by the metal, the thickness of the metal at the edge of the trench becomes so thin or disconnects there in the extreme condition.
Accordingly, a method to fill the trench with a resin has been proposed. However, in the case that the resin fills the trench, the adhesion between the wiring for the upper electrode and the resin becomes a subject. Further, the current supplied in the mesa portion to emit light sometimes reaches some thirty or forty milli-ampere, which generates heat in the mesa portion. When the resin fills in the trench formed in both sides of the mesa portion, the heat generated in the mesa portion may be effectively dissipate therefrom because the thermal conductivity of the resin usually smaller than that of the semiconductor materials.
Therefore, the present invention is to provide a method for manufacturing a semiconductor optical device that reduces the parasitic capacitance between the substrate and the electrode, and to provide the semiconductor optical device.